This invention relates to a conveying apparatus for displacing articles having at least one substantially flat side along a transport surface in different directions. Such apparatuses typically comprise a plurality of driven transport wheels each suspended for rotation about a centerline thereof and for pivotal movement about an associated steering axis directed perpendicularly to the transport surface.
From French patent application 2 407 150 an apparatus is known which, for driving rotation of the transport wheels about the centerlines thereof is provided with a string passing over a driving sheave, driven sheaves and, between the driving sheave and one of the driven sheaves, at least one divert roller. The driven sheaves and the divert roller are each associated with one of the transport wheels and the driven sheaves are pivotable along with the associated transport wheel about the associated steering axis.
In such a conveying apparatus an article to be displaced along the transport surface is supported by the transport wheels. The article can be displaced by driving the transport wheels, so that they rotate about their centerlines. Changing the direction of transport is possible by pivoting the transport wheels about the associated steering axes directed perpendicularly to the transport surface.
Each of the transport wheels mentioned is drivable by means of the string. The driven string sheave, which, along with an associated transport wheel, is pivotable about the steering axis, can be displaced relative to the driving string sheave, which itself is exclusively rotatable about its centerline. The driving string permits a certain angular displacement of the centerlines of the driving and the driven string sheaves relative to each other, so that the transport wheels can be steered through the same angle.
The endless string extends from the driving sheave over a first one of the divert rollers to a gutter in the transport wheel which forms the driven sheave. From the driven sheave the string passes over another one of the divert rollers and meets the driving sheave in a position opposite the position from where it extended to the first one of the divert rollers. Then the string passes over still another one of the divert rollers to another one of the transport wheels and then via still another one of the divert rollers back to the driving sheave. Thus two axially spaced transport wheels are driven by a single string.
A drawback of this known apparatus is that the length of the string increases considerably according as the angle between the axes of a driving string sheave and an associated driven string sheave increases. In order to permit such elongation, the string should have a considerable elasticity, which, however, is at the expense of the accuracy of the drive of the transport wheel and of the forces to be transmitted.
A further drawback of this known apparatus is that the string, when the centerlines of the driving and the driven string sheaves have been displaced relative to each other, shifts in axial direction over the driving string sheave as it is rotating. This causes a considerable wear of the string.